Titanium dioxide is widely used in various fields as white pigments, UV shielding materials, photocatalyst materials, etc. Specifically, exterior use utilizing titanium oxide with suppressed photocatalytic property, such as exterior walls for buildings, coating compositions for buildings, or parts or coating compositions for automobiles, has been recently increased. These materials used in such applications are required to have high weather resistance and endurance since these are exposed to the elements over a long period. Titanium dioxide is sometimes blended in a fluorine material having excellent heat resistance and high chemical resistance to enhance weather resistance and endurance.
Photocatalytic action by titanium oxide, however, decomposes not only organic substances which causes stains but also necessary organic components in a coating composition, a resin composition, etc., which leads to discoloration, fading, and deterioration of coating compositions and materials. As a result, weather resistance and endurance of parts deteriorate in some cases.
Thus, some studies have been made so far for suppressing photocatalytic activity of a material containing titanium dioxide by providing a coating layer of oxides on the surface of titanium dioxide particles to thereby enhancing weather resistance of the titanium dioxide particles.
For example, Patent Literature 1 discloses a method of producing weather-resistant titanium dioxide by depositing a coating layer of high-density silica on the surface of the titanium dioxide, and then depositing alumina thereon.
Patent Literature 2 discloses a method for improving photochemical stability of titanium dioxide by forming a layer that consists of porous hydrous silica and alumina hydrate on the surface of TiO2, calcining the TiO2, and then further forming a hydrous metal oxide layer that comprises at least one metal selected from the group consisting of silicon, zirconium, and aluminum.